A deep understanding of the nuances of air quality regulations and permitting issues is critical to keeping facilities safe, operational and in compliance. This can be a daunting task when a project faces a range of regulations and permitting requirements — as well as the goal to keep a project moving forward seamlessly.

One unique solution that supports permit applications for the construction or modification of facilities is air dispersion modeling. A modeling assessment evaluates the estimated emissions, supports the air permit application and predicts ambient air impacts from the facility’s emission sources. Air dispersion modeling can identify impacts from contaminants and assist in developing effective strategies to minimize impacts, allowing owners and operators to secure the necessary permits while meeting construction schedules. It is a streamlined method to determine whether a project will have significant adverse impacts on the air quality, soils, vegetation, visibility or growth in the surrounding areas. An experienced air dispersion modeler can establish an effective permitting strategy and smooth permitting process, while saving the client’s time and money.

Rather than installing a monitor at the site — a lengthy and costly process — to determine the emitted concentration for a specific pollutant from a facility, an air dispersion model relies on mathematical formulations to characterize the atmospheric processes that disperse a pollutant emitted by a facility source. The model takes emissions and meteorological inputs and uses them to predict concentrations at selected downwind receptor locations. These models are then used to determine compliance with National Ambient Air Quality Standards and other regulatory or state requirements.

On a recent project, our team completed an air dispersion modeling analysis to assess the deposition impacts of per- and polyfluoroalkyl substances (PFAS) from three proposed aerators for leachate treatment ponds at a landfill. During the review of the permit application, a regulatory agency wanted to quantify any impacts of PFAS deposition from aerator operation on a lake about 2,700 feet southeast of the treatment ponds. We used AERMOD — a steady-state air dispersion model approved by the U.S. Environmental Protection Agency — to estimate downwind ground-level concentrations from multiple sources using detailed meteorological data. The modeling analysis showed that PFAS testing at the lake was not necessary since PFAS impacts from the aerators would be minimal.

On another project, a major utility needed to identify alternate methods to treat its wastewater streams with less costly and labor-intensive systems. Air dispersion modeling was performed to fully understand the impacts of downdraft spray evaporators. This air dispersion study evaluated the plume and particle dispersion while considering weather patterns. These models often apply the most conservative operational conditions to determine if the selected operating conditions will result in compliance with the modeling thresholds.

Modeling these unique situations expedites the permitting process and provides a baseline to define a project approach. This upfront investment can help owners and operators save time and money without compromising the project schedule.


Ever-changing air quality regulations can create complexities for projects. Experienced air quality teams offer a strong foundation for identifying and executing compliance strategies that address specific project needs.

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Minda Nelson, PE, is an associate environmental engineer at Burns & McDonnell who specializes in air quality permitting and air dispersion modeling. She works closely with industrial and utility clients to acquire operating and construction air permits, while also conducting regulatory interpretations, emission calculations and other critical air permitting issues. Over her 16-year career, she has completed more than 70 air dispersion modeling projects in multiple industries.